System and method for compensating polarization-dependent sensitivity of dispersive optics in a rotating analyzer ellipsometer system

ABSTRACT

An ellipsometer system which includes a pivotal dispersive optics positioned to receive polychromatic light from an analyzer thereof, without further focusing after reflection from a substrate system, is presented. In addition, a rotating compensator, positioned between the analyzer and the dispersive optics, which serves to reduce detector element polarization dependent sensitivity to light entering thereto after it interacts with the dispersive optics, is disclosed. The method of the present invention can include application of mathematical correction factors to, for instance, substrate system characterizing PSI and DELTA values, or Fourier ALPHA and BETA coefficients.

The present application is a Continuation-In-Part of application07/947,430, filed 9/18/92, now U.S. Pat. No. 5,373,359.

TECHNICAL FIELD

The present invention relates to ellipsometer systems and methods ofuse. More particularly the present invention is a system and method ofuse for compensating and correcting polarization-dependent sensitivityin rotating analyzer ellipsometer systems.

BACKGROUND

Null and spectroscopic ellipsometer systems for use in investigation andcharacterization of physical and optical properties of substrate systemsare well known. Briefly, such systems operate by monitoring changeseffected in the polarization state of a beam of light when said beam oflight is caused to interact with a substrate system. Spectroscopicellipsometer systems, including those which utilize phase modulation andRotating Analyzers, (ie. rotating analyzer ellipsometer systems,hereinafter (RAE)), are widely applied because they provide improvedtheoretical precision and high optical efficiency, hence, can beutilized with weaker polychromatic sources of light as compared to nullellipsometer systems. Spectroscopic ellipsometer systems are also fasterand easier to use. However, use of spectroscopic ellipsometer systemsrequires increased attention to compensation necessitated by, forinstance, Polarization-Dependent Sensitivity, (hereinafter, (PDS)) inresponse to applied polychromatic light. Compensation of (PDS) can beapproached in two mathematically oriented ways, one of which requirescorrection of numerous raw data points obtained during investigation ofa substrate system by a spectroscopic ellipsometer system, (eg. an RAE),and the second of which applies correction factors to, for instance,Fourier Coefficients, (termed ALPHA and BETA), derived by application ofFourier Analysis to said numerous raw data points. Of said approaches,the second is generally easier to perform and is preferred.

To understand the second approach to mathematically. compensating (PDS)it must be appreciated that the end goal of applying ellipsometry to asubstrate system is simultaneous characterization of the physical andoptical properties of said substrate system. Two ellipsometric constant,(at a particular light beam wavelength and angle of incidence on saidsubstrate), parameters, PSI and DELTA serve to provide saidcharacterization. Calculation of PSI and DELTA, however, is typicallyintermediated by the calculation of Fourier Coefficients, ALPHA andBETA, as alluded to above. Said Fourier Coefficients, ALPHA and BETA,are related to PSI and DELTA by known mathematical relationships.Briefly, to compensate for system (PDS), ALPHA and BETA can be correctedprior to application of the mathematical relationships which interrelatethe Fourier Coefficients ALPHA and BETA, to PSI and DELTA. It is notedthat ALPHA and BETA correction factors are typically derived during anellipsometer system calibration procedure. It is mentioned that directcorrection of PSI and DELTA is a variation on said mathematicalapproach.

As mentioned, PSI and DELTA are constants of a substrate system, but asalso mentioned, said constants vary with the wavelength of a beam oflight applied to a substrate system by an ellipsometer system. This isbecause ellipsometer system elements, (eg. dispersive optics), as wellas investigated substrate systems, typically respond differently todifferent wavelengths of light. (Note, see the Disclosure of theInvention and Detailed Description Sections in this Disclosure forinsight as to the elements, and their configuration, which comprise atypical. ellipsometry system). As a result, an ellipsometer system whichperforms a substrate system analysis at a multiplicity of wavelengthsmust provide appropriate ALPHA and BETA (PDS) correction factors foreach of said multiplicity of wavelengths utilized, (assuming the secondapproach to compensating (PDS) identified above is utilized).

Continuing, it is to be appreciated that while compensation can beaccomplished based upon a purely mathematical approach, correctionfactors can become a significant percentage of an ALPHA or BETA value atcertain corresponding PSI and DELTA values. When this occurs,application of a correction factor can result in relatively smallcorrected ALPHA and/or BETA values, which values can be on the order ofsystem background noise. This results in reduced sensitivity, (ie.reduced ability to calculate accurate PSI and DELTA values from saidcorrected ALPHA and BETA values), at said certain corresponding PSI andDELTA values. It should then be apparent that a system element whichwould reduce the magnitude of required ALPHA and BETA correction factorswould provide utility. A similar situation exists when PSI and DELTA aredirectly corrected.

It is also mentioned that (RAE's) often comprise elements, (eg.photodetectors), which react nonlinearly with respect to differentintensities and wavelengths of light. The above outlined mathematicalapproach to compensation can be used in such (RAE's) to simultaneouslycompensate both (PDS) and said nonlinearities.

Continuing, the present invention teaches that a (RAE) in which adiffraction grating comprises a dispersive optics system element, whichdiffraction grating is situated prior to a detector element and servesto provide a multiplicity of independently detectable light wavelengthbeams to said detector element, should have (PDS) response wavelengthdependence reduced by application of a specific system element to said(RAE), and by practice of a specific method of use thereof. The presentinvention method of use includes the teaching that compensation of said(RAE) (PDS) can be further effected by mathematical application of ALPHAand BETA correction factors, or by direct mathematical correction of PSIand DELTA values.

A search of relevant references has provided an article by Russev, App.Optics, Vol. 28, No. 8, Apr. 1989, p. 1504-1507. An approach tomathematically calculating ALPHA and BETA correction factors tocompensate for (PDS) and/or detecting system nonlinearity, eitherindependently or simultaneously, is described in said reference. Aswell, said reference mentions the use of a depolarizer between arotating analyzer and a detector as a means of reducing (PDS), but notesthat said approach is not complete because of residual beampolarization. In addition, the presence of a depolarizer is stated to beundesirable because it reduces light flux reaching the detector.

In view of the approach described in the Russev reference, it is notedthat an article by Johs, Thin Solid Films, 234(1993), p. 395-398,describes an improved approach to determining and applying ALPHA andBETA correction factors using a regression data fitting approach over alarge range of polarizer azimuth angles.

The Russev and Johs articles cited above are incorporated by referenceinto this Disclosure.

A U.S. Pat. No. 4,837,603 to Hayashi, describes a method of correctingazimuth angle of photometric ellipsometers by an approach whichmathematically corrects PSI and DELTA. Said reference is alsoincorporated by reference into this Disclosure.

An article by Stobie et al., J. Opt. Soc. Am. 65, p. 25 (1975),describes application of a double modulation which could be used tocircumvent (PDS) of dispersive optics. The system requires that apolarizer, (ie. polarization state generator), and an analyzer (ie.polarization state detector), be set at known azimuths, and that arotating analyzer, (ie. modulator), be present before or after a sample.As it is difficult, however, to determine azimuths of a polarizer andanalyzer, their being nonlinear functions of ellipsometric measurementparameters, use of the ellipsometer system described in said referenceis relatively complex and in some applications unsuitable forapplication to spectroscopic ellipsometer systems because sensitivity tocertain values of PSI and DELTA is reduced. It is noted that the Stobieet al. article fails to suggest that the system described therein shouldbe used to compensate (PDS).

An article by Collins, Rev. Scien. Inst., 61(8), August 1990, p.2029-2062, describes an ellipsometer system which uses a rotatingpolarizer. Said system could be used to remove (PDS) of dispersiveoptics but introduces (PDS) to the system light source. In said systeman analyzer is set at a known azimuth and modulation is introduced inthe polarization state generator. Said configuration requirescalibration of residual light source polarization, and light beamprecession on the sample can occur during use. This is especiallyunsuitable wherein monitoring of a real time, in situ process isinvolved. As well, the Collins article fails to suggest use of thesystem described therein to compensate (PDS).

The above discussion should serve to demonstrate that a system, andmethod of use thereof, which can easily, simply and efficiently serve toreduce (PDS) would provide utility. Such a system and method of use aretaught by the present invention.

DISCLOSURE OF THE INVENTION

The present invention assumes the presence of a Rotating AnalyzerEllipsometer System, (RAE), such as that taught in copending patentapplication Ser. No. 07/947,430, which has issued as U.S. Pat. No.5,373,359. Briefly, said (RAE) is comprised of a sequential functionalcombination of a Light Source, (LS) and a Polarization State Generator,(PSG). Said (RAE) is further comprised of a sequential functionalcombination of a Rotating Analyzer, (RA), a Dispersive Optics, (eg. aDiffraction Grating (DG)), and a Photodetector Array, (PA).

In use said (LS) provides a beam of polychromatic light to said (PSG)and said (PSG) effects an intended polarization state thereof. Said beamof polychromatic light in said intended polarization state is thencaused to interact with, and reflect from, a Substrate System, (SS),which interaction causes an alteration in the polarization state of saidbeam of polychromatic light. Said altered polarization state beam ofpolychromatic light is then caused to pass through said (RA) and emergeas linearly polarized. Said linearly polarized beam of polychromaticlight is then caused to interact with and reflect from said (DG) whereata diffracted multiplicity of essentially single wavelength beams oftypically elliptically polarized light are caused to form, each of whichessentially single wavelength beam of typically elliptically polarizedlight is caused to be directed so as to enter a separate DetectorElement, (DE), of said (PA). Said (DE's) are oriented at predeterminedangles with respect to said (DG) and said (DG) can be rotated to set theangle of incidence of said linearly polarized beam of light thereon,with respect to a normal to said (DG), to within plus or minus one-half(0.5) a degree. Said (DE's) are typically, but not necessarily,photodiodes which can provide essentially linear output signal versesinput light intensity characteristics over an operating wavelengthspectra. Each of said (DE's) serve to detect the intensity of areceived, essentially single wavelength beam of typically ellipticallypolarized light entering thereto, as a function of time. Proper analysisof said intensity verses time data can provide PSI and DELTA constants,(at the specific light beam wavelength detected by a (DE)), of a (SS),as described in the Background Section of this Disclosure. A problem inthe operation of the described (RAE) exists, however, in that said (DG)causes different effects on linearly polarized light beams of differentwavelengths. That is, the (DG) introduces Polarization-DependentSensitivity (PDS) error. The present invention is in part an additional(RAE) system element, termed a Rotating Compensator, (RC), which incombination with a Rotating Analyzer(RA) comprises a Rotating AnalyzerCompensator Assembly system (RACA), the presence of which in said (RAE),during use thereof, serves to reduce (DG) introduced (PDS) error.

The present invention teaches that a (RAE) should be modified so as tofunctionally include a Rotating Compensator, (RC), such that during usesaid (RC) is fixed with respect to the azimuth of said (RA), saidcombination of (RA) and (RC) effecting a simultaneously RotatingAnalyzer Compensator Assembly system, (RACA). It is possible for said(RACA) to be realized as a functionally interconnected system comprisedof a physically independent (RA) and a physically independent (RC), butit is specifically noted and emphasized that in the preferred embodimentof the present invention, the (RACA) comprises a (RA) and a (RC) whichare physically, as well as functionally, integrated as a single systemelement.

The purpose of said (RACA) is to accept a polychromatic beam oftypically elliptically polarized light, provide linearly polarized lightemerging from said (RA), and cause said linearly polarized light to beconverted to a polychromatic beam of light in an elliptical, preferablyessentially circularly, polarized form, prior to being caused tointeract with and reflect from, in a diffracted form, said (DG) as amultiplicity of essentially single wavelength elliptically polarizedbeams of light.

The end effect of the presence of said (RC) in said (RACA), and theincorporated method of its use, is to reduce (PDS) introduced by said(DG) because the (DG) does not introduce as much (PDS) to anelliptically polarized beam of light as it does to a linearly polarizedbeam of light. That is, the (DG) operates, (eg. rotates light beamcomponents), more consistently over a spectrum of wavelengths whenincident elliptically polarized beams of light are present, than it doesover the same spectrum of wavelengths when incident linearly polarizedbeams of light are present.

The present invention also teaches that Fourier Coefficient, ALPHA andBETA, correction factors as mentioned in the Background Section andreferences cited therein (eg. Russev and Johs articles), can be derivedfor each essentially single wavelength of elliptically polarized light,and applied to measured ALPHA and BETA values, to effect full (PDS)compensation. When this is done a correction factor application means,(eg. a computing system), in combination with said (RAE), is utilized.Briefly, a series of raw ALPHA and BETA values are measured as afunction of a series of (PSG) azimuths. An equation is then fit to saiddata utilizing a Mean Square Error criteria to obtain corrected ALPHAand BETA. The signals measured by the (DE's) are of the form:

    I.sub.D (t)=I.sub.0 (1+α.sub.measured cos 2ωt+β.sub.measured sin 2ωt)

For a "perfect" or ideal system the following equations predict thenormalized Fourier Coefficients, as a function of ellipsometricparameters of the sample (eg. PSI and DELTA), the normalized inputpolarizer angle (P), and the azimuthal offset or calibration angle forthe input polarizer (Ps): ##EQU1## The first correction to thesecoefficients is due to (PDS). The magnitude of the (PDS) at a particularwavelength is given by "f", and the azimuthal angle of the (PDS) isgiven by "Fd". Denoting:

    x=(1-f.sup.2)/(1+f.sup.2)

    x.sub.c =x cos(2 F.sub.d)

    x.sub.s =x sin(2 F.sub.d)

The (PDS) corrections are then applied to the ideal coefficients:

    α'=(α.sub.ideal +x.sub.c)/[1+0.5(αx.sub.c +βx.sub.s)]

    β'=(β.sub.ideal +x.sub.s)/[1+0.5(αx.sub.c +βx.sub.s)]

Finally, the standard (RAE) calibration const:ants for the analyzerazimuth (As) and the electronic attenuation factor (η) are introduced tocomplete the calculation of the predicted Fourier Coefficients, whichshould be the same as the measured Fourier Coefficients, when all of thecalibration constants have been accurately determined:

    α.sub.measured ≅α.sub.predicted =(1/η)[α'cos(2 As)-β'sin(2 As)]

    β.sub.measured ≅β.sub.predicted =(1/η)[α'sin(2 As)+β'cos(2 As)]

Similarly, mathematical correction of PSI and DELTA values can beperformed, such as described in U.S. Pat. No. 4,837,603, for instance.

The present invention will be better understood by reference to theDetailed Description Section of the present Disclosure, in conjunctionwith the Drawings.

SUMMARY OF THE INVENTION

Rotating Analyzer Ellipsometry (RAE) systems which utilize polychromaticlight and which utilize dispersive optics to simultaneously provide amultiplicity of essentially single wavelength beams of light to separateDetector Elements (DE) in a Photodetector Array (PA) for analysisthereof, are known.

A problem associated with use of said (RAE's) is that dispersive optics,(eg. Diffraction Grating (DG)), therein introduce Polarization-DependentSensitivity (PDS). This is particularly true when polychromatic lightdiffracted thereby is other than essentially circularly polarized. Thatis, (PDS) effected by dispersive optics is less pronounced when lightincident thereon is essentially circularly polarized, or at leastelliptically polarized, than when it is in a linearly polarized state.

One approach to compensating (PDS) is by application of mathematicalcorrection factors applied to ALPHA and BETA Fourier coefficients,(which correction factors and ALPHA and BETA values are derived fromanalysis of (RAE) provided data), prior to calculating Substrate System(SS) characterizing PSI and DELTA parameter values from corrected ALPHAand BETA. Use of a purely mathematical approach, however, results inreduced sensitivities at certain PSI and DELTA values because ALPHAand/or BETA correction factors can represent a rather significantpercentage of a raw ALPHA and/or BETA at said corresponding PSI andDELTA values. Application of s,aid correction factors then providesrather small corrected ALPHA and/or BETA values which can be rather moreadversely affected by system noise. Mathematical correction of PSI andDELTA values can also be practiced, with similar accompanying problems.

Another approach to reducing (PDS) is to provide light to a (DG) whichis elliptically, and preferably essentially circularly polarized, asopposed to linearly polarized. The present invention teaches that thisshould be accomplished by effecting a functional combination of aRotating Analyzer (RA) and a Rotating Compensator (RC) to form aRotating Analyzer Compensation Assembly System (RACA) in a (RAE) suchthat a light beam entering said (RA), after being reflected from aSample Substrate (SS), exits said (RC) in an elliptically, (preferablyessentially circularly), polarized state prior to being diffracted bysaid (DG).

The present invention provides that both identified approaches, (ie. useof said (RACA) and mathematical), to reducing (PDS), can be utilized.

It is therefore a purpose of the present invention to identify animproved (RAE).

It is another purpose of the present invention to identify an improved(RAE) in which a (DG) serves as dispersive optics and in which (PDS)compensation can be relatively easily accomplished.

It is yet another purpose of the present invention to teach a relativelysimple (RAE) system element in the form of a (RC) which, in functionalcombination with a (RA), comprises a (RACA), which (RACA) during use,provides elliptically, (preferably essentially circularly), polarizedlight to a (DG) in the containing (RAE).

It is still yet another purpose of the present invention to teach theuse of a mathematical approach to compensating (PDS) in a (RAE) whichincludes a (RACA).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a rotating analyzer ellipsometer system.

FIG. 2 shows a block diagram of a rotating analyzer ellipsometer systemwhich includes a rotating compensator in functional combination with arotating analyzer.

FIG. 3 shows a perspective representation of a rotating analyzer infunctional combination with a rotating compensator.

FIG. 4 shows a graph of polarization-dependence sensitivity as afunction of light beam wavelength in a rotating analyzer ellipsometerwhich does not include a rotating compensator as indicated in FIG. 1.

FIG. 5 shows a graph of polarization-dependence sensitivity as afunction of light beam wavelength in a rotating analyzer ellipsometerwhich includes a rotating compensator as indicated in FIG. 2.

FIG. 6 shows the relative orientation of a diffraction grating and aphotodetector array, which photodetector array is shown to be comprisedof a multiplicity of detector elements.

DETAILED DESCRIPTION

Turning now to the Drawings, there is shown in FIG. 1 a RotatingAnalyzer Ellipsometer System (RAE) as disclosed in copending patentapplication Ser. No. 07/947,430. Identified are Light Source (LS),Polarization State Generator (PSG), Sample Substrate (SS), RotatingAnalyzer (RA), Diffraction Grating (DG), and Photodetector Array (PA).FIG. 6 shows the relative orientation of diffraction grating (DG) andphotodetector array (PA), which photodetector array (PA) is comprised ofa multiplicity of Detector Elements (DE's). It is noted that saidDiffraction Grating (DG) is pivotably mounted so that it can receiveincident light at desired angles with respect to the normal thereto,said angles being controllable to plus or minus one-half (0.5) a degree.

In use Light Source (LS) provides typically polychromatic light in atypically collimated form to said Polarization State Generator (PSG),from which said typically polychromatic collimated beam of light emergesin an intended polarization state. Said typically collimatedpolychromatic beam of light is then caused to impinge upon said SampleSubstrate (SS), and reflect therefrom in an altered state ofpolarization. Said reflected altered polarization state beam of lightreflecting from said Sample Substrate (SS) is then caused, withoutadditional focusing, to pass through said Rotating Analyzer (RA) fromwhich it emerges in a linearly polarized form, then reflects from saidDiffraction Grating (DG) in a diffracted state comprising a multiplicityof essentially single wavelength typically elliptically polarized beamsof light; at least some of which are caused to enter specific wavelengthassociated Detector Elements (DE's) in said Photodetector Array (PA),wherein analysis of the intensity thereof is performed with respect totime. It is noted that Photodetector Array (PA) Detector Elements (DE's)which have linear intensity verses signal output characteristics, suchas photodiodes, are preferred. Utilizing said linear characteristicDetector Elements (DE's) eliminates complications associated with useof, for instance, photomultiplier tubes as detectors.

While the above described Rotating Analyzer Ellipsometer system (RAE)provides benefits, a problem has been found to exist during use in thatsaid Diffraction Grating (DG) introduces wavelength sensitivePolarization-Dependent Sensitivity (PDS). That is, the DiffractionGrating (DG) responds differently to linearly polarized light ofdifferent wavelengths, and introduces different Polarization-DependentSensitivity (PDS) errors to the various of said multiplicity ofessentially single wavelength typically elliptically polarized beams oflight diffracted therefrom.

A mathematical approach to compensating said Polarization-DependantSensitivity (PDS) involves obtaining and applying correction factors toALPHA and BETA Fourier Coefficients derived by applying Fourier Analysisto raw data obtained from Photodetector Array (PA) Detector Elements(DE's), prior to calculating Sample Substrate (SS) constants PSI andDELTA for each detected essentially single wavelength typicallyelliptically polarized beam of light. (Note that PSI and DELTA valuesare calculated from corrected ALPHA and BETA's). This approach is betterdescribed in Background Section cited references, (eg. Russev and Johsarticles), which are incorporated herein by reference. As well, PSI andDELTA values can be directly mathematically corrected by an approach,for instance, as described in U.S. Pat. No. 4,837,603 also referenced inthe Background Section of this Declaration.

The present invention, however, teaches that Polarization-DependentSensitivity (PDS) should be simultaneously reduced in a multiplicity ofessentially single wavelength beams of light reflected and diffractedfrom said Diffraction Grating (DG), by addition of an element to theRotating Analyzer Ellipsometer System (RAE) of FIG. 1. Said additionalelement is termed a Rotating Compensator (RC) and is indicated in FIG. 2as being part of a functional combination of a Rotating Analyzer (RA)and said Rotating Compensator (RC), which together comprise a RotatingAnalyzer Compensator Assembly System (RACA). FIG. 3 better shows thatsaid Rotating Analyzer Compensator Assembly System (RACA) is preferablya single system element comprised of a Rotating Analyzer (RA) and aRotating Compensator (RC) in fixed geometric functional relationship toone another. In use a beam of light entering said Rotating Analyzer (RA)passes therethrough, then passes through said Rotating Compensator, (RC)prior to being caused to impinge upon and reflect from, in a diffractedform, said Diffraction Grating (DG). It will be recalled that lightexiting said Rotating Analyzer (RA) is linearly polarized. The purposeof the Rotating Compensator (RC) is to alter said polarization statethereof to elliptical, and preferably, to essentially circular. Thereason being that a Diffraction Grating (DG) introduces lessPolarization-Dependent Sensitivity (PDS) to elliptically and essentiallycircularly polarized light than it does to linearly polarized light. Itis also to be understood that Detector Elements (DE) can introducePolarization-Dependent Sensitivity in a Rotating Analyzer EllipsometerSystem (RAE). The present invention system and method can also beutilized to compensate such. It is emphasized that the describedRotating Analyzer Compensator Assembly system (RACA), and the method ofits use in a Rotating Analyzer Ellipsometer (RAE) are focuses of thepresent invention.

It is further noted that while not a limitation of the presentinvention, in the preferred embodiment of the present invention, theRotating Compensator (RC) is oriented at an angle of forty-five (45)degrees with respect to the azimuth of the Rotating Analyzer (RA).

Turning now to FIG. 4, there is provided a graph ofPolarization-Dependent Sensitivity (PDS) verses Light Beam Wavelengthprovided by a Rotating Analyzer Ellipsometer System (RAE) as shown inFIG. 1. FIG. 5 shows a similar graph of Polarization-DependentSensitivity (PDS) for a Rotating Analyzer Ellipsometer System (RAE) asshown. in FIG. 2. The reduction in Polarization-Dependent Sensitivity(PDS) demonstrated in FIG. 5 as compared to FIG. 4, (centered at a lightbeam wavelength of approximately six-thousand-three-hundred (6300)Angstroms for the example shown), is a direct result of the presence ofthe Rotating Compensator (RC) identified in FIGS. 2 and 3.

It is noted that a suitable Rotating Compensator (RC) can be embodiedusing Helles Griot or CVI Optics Corporation quarter wavelength, (ninety(90) degree), Mica Retardation Plates. For example Melles Griot ProductNo. 02 WRM 001 or 02 WRM 011 and the like are identified.

The present invention teaches that the mathematical approach tocompensating for Polarization-Dependent Sensitivity (PDS) mentionedabove can also be applied to Fourier Coefficients obtained from analysisof data provided by the present invention embodiment which includes theRotating Compensator (RC), as indicated in FIG. 2. It is therefore to beappreciated that the method of the present invention provides thatfurther Polarization-Dependent Sensitivity compensation by mathematicalcorrection of Fourier Coefficients APLHA and BETA described elsewhere inthis Disclosure can be applied to data represented in FIG. 5 to providefully compensated Polarization-Dependent Sensitivity (PDS). The benefitprovided by the presence of the Rotating Compensator (RC) of the presentinvention then, is that its use greatly reduces required mathematicalcompensation. As described in the Background Section, this decreases PSIand DELTA reduced sensitivity problems.

It is mentioned that the terminology "Substrate System" and "(SS)" havebeen used throughout this Disclosure. Said terminology is to beunderstood to include any substrate, with or without one or more filmsatop thereof, and any container for a substrate etc. which can beanalyzed by a (RAE).

The terminology "Photodetector Array" and "(PA)" has also been usedthroughout the Disclosure. Said terminology is to be understood toinclude, but is not limited to, Photodiode Arrays.

The terminology "essentially single wavelength" has been used throughoutthis Disclosure. It is to be understood that light from a DispersionOptics is a continuium of wavelengths, but that physical restraints ondetecting such light by necessity involves Finite Dimension DetectorElements, each of which detects a small range of wavelengths in saidcontinuium thereof, which small range of wavelengths is centered at somewavelength. The terminology "essentially single wavelength" refers tosaid wavelength about which the small range of wavelengths is centered,in combination with the immediately surrounding slightly larger orsmaller wavelengths. In the limit, an essentially "single" wavelengthcould be theoretically envisioned as present.

In addition, it is to be understood that the terminology. "PolychromaticLight" is inclusive of "white light."

The terminology "Rotating Analyzer" is to be understood to mean arotating polarization analyzer.

The terminology "Rotating Compensator" is to be understood to mean, forinstance, a ninety (90) degree, (ie. quarter wavelength), retardationplate.

The terminology "Diffraction Grating" and "(DG)" are used throughoutthis disclosure. It is to be understood that said terminology identifiesa particularly relevant, but not limiting, example of a DispersiveOptics.

Finally, the terminology "essentially circular" has been usedthroughtout this Disclosure. As the difference between "essentiallycircular" and "elliptical", as said terms are understood by thoseskilled in the art of ellipsometry is subjective and open tointerpretation, it is to be understood that said terminology should beinterpreted, where appropriate, to mean "elliptical" with the optimumstate being "circular".

Having hereby disclosed the subject matter of the present invention, itshould be obvious that many modifications, substitutions and variationsof the present invention are possible in light of the teachings. It istherefore to be understood that the present invention can be practicedother than as specifically described, and should be limited in breadthand scope only by the claims.

We claim:
 1. A spectroscopic ellipsometer for use in sensingcharacteristics of a sample substrate system comprising:a. a lightsource; b. a polarization state generator; c. an analyzer; and d. adiffraction grating positioned so as to receive a beam of polychromaticlight which passes through the analyzer without further focusing aftersaid beam of polychromatic light, which originates in said light source,reflects from a substrate system; wherein said diffraction gratingreflects incident polychromatic light onto a photodetector array at apredetermined angle with respect to the normal to the diffractiongrating, with a precision of at least plus or minus one-half degree. 2.A rotating analyzer ellipsometer system comprising:a. a light source; b.a polarization state generator; c. a rotating analyzer; d. a diffractiongrating; and e. a photodetector system;such that, during use, a beam ofpolychromatic light from said light source is caused to pass throughsaid polarization state generator and is then caused to be reflectedfrom a substrate system, thereby becoming a typically ellipticallypolarized beam of light; such that said typically elliptically polarizedpolychromatic beam of light is, without further focusing, caused to passthrough said rotating analyzer and become linearly polarized, whichlinearly polarized polychromatic beam of light emerging from saidrotating analyzer is then caused to be incident upon said diffractiongrating at an intended angle to a normal thereto, precise to plus orminus one-half degree, and reflect in a diffracted form therefrom as amultiplicity of essentially single wavelength beams of light, each ofwhich essentially single wavelength beams of light enters a separatedetector element of said photodetector system for analysis therein.
 3. Arotating analyzer ellipsometer system as in claim 2 which furthercomprises a rotating compensator in functional combination with saidrotating analyzer, such that said linearly polarized polychromatic beamof light which emerges from said rotating analyzer is caused to passthrough said rotating compensator and emerge therefrom as other than alinearly polarized polychromatic beam of light prior to reflecting in adiffracted form from said diffraction grating.
 4. A spectroscopicellipsometer for use in sensing characteristics of a substrate system,comprising:a. a light source; b. a polarization state generator; c. ananalyzer; and d. a dispersive optics positioned so as to receive a beamof polychromatic light passing through said analyzer, without furtherfocusing after said beam of polychromatic light, which originates insaid light source, reflects from a substrate system; wherein saiddispersive optics directs incident polychromatic light onto aphotodetector array at a predetermined angle with respect thereto, theangle at which incident polychromatic light is directed from saiddispersive optics, with respect to a normal thereto, being precise towithin plus or minus one-half a degree.
 5. A spectroscopic ellipsometerfor use in sensing characteristics of a substrate system, comprising:a.a light source; b. a polarization state generator; c. an analyzer; andd. a dispersive optics positioned so as to receive a beam ofpolychromatic light passing through said analyzer, without furtherfocusing after said beam of polychromatic light, which originates insaid liqht source, reflects from a substrate system; wherein saiddispersive optics directs incident polychromatic light onto aphotodetector array at a predetermined angle with respect thereto, inwhich spectroscopic ellipsometer the dispersive optics is apolychromatic light reflecting diffraction grating and the angle whichincident polychromatic light is reflected therefrom, with respect to anormal thereto, is precise to within plus or minus one-half degree.
 6. Arotating analyzer ellipsometer system comprising:a. a light source; b. apolarization state generator; c. a rotating analyzer; d. a dispersiveoptic; and e. a photodetector system;such that, during use,polychromatic light from said light source is caused to pass throughsaid polarization state generator and is then caused to reflect from asubstrate system, thereby becoming a typically elliptically polarizedbeam of light; such that said typically ellipticallypolarized-polychromatic light is, without further focusing, caused topass through said rotating analyzer and become essentially linearlypolarized, which essentially linearly polarized polychromatic lightemerging from said rotating analyzer is then caused to be incident uponsaid dispersive optics at an intended angle to a normal thereto, and bedirected therefrom at an angle with respect to a normal thereto which isprecise to within plus or minus one-half a degree, and proceed therefromas a multiplicity of essentially single wavelength beams of light, eachof which essentially single wavelength beam of light enters a separatedetector element of said photodetector system for analysis therein.
 7. Arotating analyzer ellipsometer as in claim 6, in which the photodetectorsystem is a photodiode array comprising a plurality of detectorelements.
 8. A rotating analyzer ellipsometer system as in claim 6 whichfurther comprises a rotating compensator in functional combination withsaid rotating analyzer, such that said essentially linearly polarizedpolychromatic light which emerges from said rotating analyzer is causedto pass through said rotating compensator and emerge therefrom as otherthan linearly polarized prior to encountering said dispersive optics. 9.A rotating analyzer ellipsometer system as in claim 8 in which there isa fixed angle between the azimuth of said analyzer and the azimuth ofsaid compensator of forty-five (45) degrees.
 10. A rotating analyzerellipsometer system as in claim 8, in which there is an angle betweenthe azimuth of said analyzer and the azimuth of said compensator ofother than forty-five (45) degrees.
 11. A rotating analyzer ellipsometeras in claim 8 in which the rotating analyzer and rotating compensatorcomprise a functionally, and physically combined single rotatinganalyzer-compensator system.
 12. A rotating analyzer ellipsometer as inclaim 8 in which the rotating analyzer and the rotating compensator arephysically separate systems.
 13. A rotating analyzer ellipsometer systemcomprising:a. a light source; b. a polarization state generator; c. arotating analyzer; d. a dispersive optic; and e. a photodetectorsystem;such that, during use, polychromatic liqht from said light sourceis caused to pass throuqh said polarization state generator and is thencaused to reflect from a substrate system, thereby becoming a typicallyelliptically polarized beam of light; such that said typicallyelliptically polarized polychromatic liqht is, without further focusingcaused to pass through said rotating analyzer and become essentiallylinearly polarized, which essentially linearly polarized polychromaticliqht emerging from said rotating analyzer is then caused to be incidentupon said dispersive optics at an intended angle to a normal thereto,and proceed therefrom as a multiplicity of essentially single wavelengthbeams of light, each of which essentially single wavelength beams oflight enters a separate detector element of said photodetector systemfor analysis therein, in which rotating analyzer ellipsometer system thedispersive optics is a polychromatic light reflecting diffractiongrating and the angle at which incident polychromatic light is reflectedtherefrom, with respect to a normal thereto, is precise to within plusor minus one-half degree.
 14. A method of reducingpolarization-dependence sensitivity of dispersive optics in rotatinganalyzer ellipsometer systems, comprising the steps of:a. providing arotating analyzer ellipsometer system comprising:a. a light source; b. apolarization state generator; c. a rotating analyzer; d. a rotatingcompensator; e. a dispersive optics; and f. a photodetector system;suchthat, during use, polychromatic light from said light source is causedto pass through said polarization state generator and is then caused toreflect from a substrate system, thereby becoming typically ellipticallypolarized light; such that said typically elliptically polarizedpolychromatic light is, without further focusing, caused to pass throughsaid rotating analyzer and become essentially linearly polarized, whichessentially linearly polarized polychromatic light emerging from saidrotating analyzer is then caused to pass through said rotatingcompensator, such that said linearly polarized light which exits saidrotating analyzer is caused, by passage through said rotatingcompensator, to become other than linearly polarized, which other thanlinearly polarized beam of light which emerges from said rotatingcompensator is then caused to interact with said dispersive optics andemerge therefrom as a multiplicity of essentially single wavelengthbeams of light, each of which enters a separate detector element of saidphotodetector system for analysis therein; b. causing polychromaticlight to emerge from said light source and reflect from said substratesystem, proceed through said rotating analyzer and rotating compensator,without further focusing after reflecting from said substrate system,and interact with said dispersive optics such that a multiplicity ofessentially single wavelength, other than linearly polarized, beams oflight are produced and directed from said dispersive optics at an anglewith respect to a normal thereto which is precise to within plus orminus one-half a degree; and c. causing at least some of saidmultiplicity of essentially single wavelength, other than linearlypolarized beams of light produced to enter said photodetector system foranalysis therein.
 15. A method of reducing polarization-dependencesensitivity of dispersive optics in rotating analyzer ellipsometersystems as in claim 14, which further comprises the steps of:a.additionally sensing at least some of said multiplicity of other thanlinearly polarized beams of light which emerge from said dispersiveoptics, and determining mathematical correction factors based thereon;and b. utilizing said mathematical correction factors via correctionfactor application means, to mathematically correctpolarization-dependent sensitivity.